Volume 2, Issue 6 (June 2005)
Cement-Admixture Interactions Related to Aluminate Control
Proper aluminate control has a strong effect on the performance of most portland cement based mixtures. Insufficient aluminate control typically results in poor admixture dosage efficiency, loss of workability, and in extreme cases abnormal retardation of strength development. The amount of soluble sulfate needed for proper aluminate control depends on the reactivity of the aluminate phases, not the nominal amount given by chemical analysis. Many admixtures impact both the reactivity of the cement phases, the dispersion and wetting of cement grains, and sometimes also the rate of dissolution of the sulfates. Hence, it is imperative that cement and admixture must be tested together in performance tests. This paper reviews some basic cement-admixture chemical interactions and presents some examples of the application of isothermal calorimetry as a performance test of the hydration kinetics of portland cement in the presence of admixtures.